1. Field of the Invention
The present invention generally relates to control device, an image forming device, a wear detecting method, a program, and a storage device, which enable early detection of wear of gears transmitting the rotation of a motor.
2. Description of the Related Art
In order to form an image having high image quality, an image forming device employs various measures. One of the measures is controlling a surface speed of an intermediate transferring belt to have a constant surface speed. When the surface speed varies while forming an image on one sheet of paper, image deformation, uneven shading, a color shift and so on are apt to occur. Therefore, there is a technique of controlling a motor such that the surface speed of the intermediate transferring belt is detected by an encoder or the like and the intermediate transferring belt may have a constant speed, as, for example, in Japanese Unexamined Patent Application Publication No. 2006-023403. In Japanese Unexamined Patent Application Publication No. 2006-023403, there is disclosed a technique of detecting a rotational angular displacement or a rotational angular speed of a driven rotating support body, which does not contribute to transmission of rotational driving force and forms a rotating support body of an intermediate transferring belt, extracting an amplitude and a phase of a belt AC component of the rotational angular displacement and the rotational angular speed having a frequency corresponding to a periodic thickness variation of the intermediate transferring belt in its peripheral direction, and controlling a driving rotating support body based on the amplitude and the phase. By this, it is possible to extract the amplitude and the phase of the belt AC component corresponding to the thickness variation in a belt peripheral direction with an arithmetic processing unit, which is relatively low in cost in comparison with the use of a Fourier transform, and to control the surface speed of the intermediate transferring belt to be constant.
As such, the surface speed can be controlled by accurately driving the motor. However, it is known that control of variation of a surface speed (for example, a range of several hundreds Hz) generated within a short time is difficult.
The variation of the surface speed of several hundreds hertz (Hz) is presumed to be caused by, for example, cogs which are components of a gear transmitting a rotational speed of the motor. For example, when the gear is excessively worn, a gap between a cog of the gear and a cog of another gear becomes large to cause large variation in the surface speed of the intermediate transferring belt. Japanese Unexamined Patent Application Publication No. 2005-221577 discloses a technique that detects excessive wear of the gear. In Japanese Unexamined Patent Application Publication No. 2005-221577, there is disclosed an image forming device which detects sudden speed variation from a high frequency component, which is obtained by statistically processing a result of a wavelet transformation of the rotational speed.
However, there is a problem in the image forming device of Japanese Unexamined Patent Application Publication No. 2005-221577 that wear of gears can be detected only in a case where the gear is excessively worn and lacks a cog. For example, it is impossible to detect the extent of variation of the surface speed caused by a slightly worn gear.
The image forming device ordinarily is not required to have image quality so high as to be affected by an engagement gap between cogs of the gears which are slightly worn. Further, gears are not worn to the extent of affecting image quality when a material of the gears is properly selected. However, the need to have high image quality has no limits, and there are many cases where further high speed and a large amount of printing are required. As a result, the engagement gaps between cogs caused by wear of gears influence the high image quality as the need for the higher image quality becomes strong. Further, wear of the gears is apt to occur as the rotational speed of the gears increases.
With respect to the need, if wear cannot be detected after a gear is excessively worn, printed materials continue to be output with gradually decreasing image quality, and a print obviously having wrong (abnormal) image quality is obtained when the wear is detected.